1. Field of the Invention
The invention relates to a high performance electrode for a spark ignition device, and more particularly to a conductive ceramic electrode for a spark ignition device comprising a transition metal carbide, nitride or carbonnitride ceramic.
2. Related Art
A spark plug is a spark ignition device that extends into the combustion chamber of an internal combustion engine and produces a spark to ignite a mixture of air and fuel. Recent advancements in engine technology are resulting in higher engine operating temperatures to achieve improved engine efficiency. These higher operating temperatures, however, are pushing the spark plug electrodes to the very limits of their material capabilities. Presently, Ni-based alloys, including nickel-chromium-iron alloys specified under UNS N06600, such as those sold under the trade names Inconel 600®, Nicrofer 7615®, and Ferrochronin 600®, are in wide use as spark plug electrode materials.
As is well known, the resistance to high temperature oxidation of these Ni-based nickel-chromium-iron alloys decreases as their operating temperature increases. Since combustion environments are highly oxidizing, corrosive wear including deformation and fracture caused by high temperature oxidation and sulfidation can result and is particularly exacerbated at the highest operating temperatures. At the upper limits of operating temperature (e.g., 1400° F.), tensile, creep rupture and fatigue strength also have been observed to decrease significantly which can result in deformation, cracking and fracture of the electrodes. Depending on the electrode design, specific operating conditions and other factors, these high temperature phenomena may contribute individually and collectively to undesirable growth of the spark plug gap and diminished performance of the ignition device and associated engine. In extreme cases, failure of the electrode, ignition device and associated engine can result from electrode deformation and fracture resulting from these high temperature phenomena. These failure modes and effects can be particularly problematic in that they frequently occur in high performance engines, such as those used in automobile racing.
High temperature sparking tips have also been employed in conjunction with the electrode materials described above. These sparking tips have been manufactured from a number of high temperature materials including platinum group metals and metal alloys, such as platinum, iridium, rhodium, palladium, ruthenium and rhenium, as pure metals and together with themselves and various other alloy constituents, such as various rare earth elements, in various alloy combinations; gold and gold alloys; tungsten and tungsten alloys and the like. High temperature sparking tips have been attached to electrodes, including center and ground electrodes, in various tip configurations using a wide variety of attachment and joining techniques, including resistance welding, laser welding, mechanical joining and the like, both separately and in various combinations. Notwithstanding the electrode performance improvements attainable through the use of high temperature sparking tips, there remain various aspects of these materials which limit their application and use in various spark ignition device configurations and applications, such as susceptibility to other and new high temperature oxidation, erosion and corrosion mechanisms, such as those associated with small amounts of calcium and phosphorus, thermal expansion mismatch with various center and ground electrode materials and other aspects, such as the high cost of these materials, which serve to limit their usefulness in various spark ignition applications.
Accordingly, there is a need for additional high performance electrodes and electrode materials having resistance to high temperature oxidation, sulfidation and related corrosive and erosive wear mechanisms, as well as having sufficient high temperature tensile, creep rupture and fatigue strength, and resistance to cracking and fracture sufficient for use in current and future spark ignition devices.